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Design 09/21/23

Impedance Table Tips

An impedance table defines all the requirements needed to tool or review a design in an easy-to-reference format. Providing a clear and concise impedance table will help reduce questions from your fabricator and avoid possible delays.

Below are simple tips and definitions that can help you accurately complete an impedance table.

  • Type: The impedance type notifies the fabricator what geometry to look for on the layers and what to model on the test coupon.

  • Impedance: This column is for the nominal impedance values that are required per trace width, per layer.

  • Tolerance: This is the tolerance on the nominal impedance value that will be accepted on the final product.

  • Layer: Only the layers that contain the routed impedance traces should be listed on the table. Listing layers where the impedance trace widths aren’t present may delay a job.

  •  Trace Width: Ensure the trace width listed on the table matches the width that is routed on the design. The impedance traces should not be routed with the same width as the non-impedance-controlled traces.

  • Trace Spacing: The trace-to-trace spacing for differential impedance should be listed.

  • Trace-to-Plane Spacing: The trace-to-plane spacing for coplanar waveguide impedance should be listed.

  • Trace Offset: The offset for broad-side coupled impedance should be listed. Best practice is to route the traces on the same core.

  • Reference Layer: This column lists the reference planes in the design that should be modeled in the coupon, per impedance type.

Example Table & Values

The examples below are not exhaustive, and only illustrate some of the common impedance types. For specific impedance questions, please reach out to your sales rep. or our FAE team ( .

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